Open Data supplied by Natural Environment Research Council (NERC)

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

RRS Charles Darwin 78 CTD Data Documentation

Introduction

Instrumentation and Methodology

Instrumentation Summary

The CTD profiles were taken with a Neil Brown Systems MkIII CTD (s/n 01-1195) mounted beneath a bottle rosette. The CTD was fitted with a pressure sensor, conductivity cell, and a platinum resistance thermometer.

Data Acquisition

Lowering speeds were about 30m/min to 50m and then slowly increased to about 60m/min to 500m.

A total of 207 casts were conducted (001 - 241). There were no casts in the numbering sequence 066 - 099.

Data Processing

The raw data were averaged down to 1db values.

Temperature

A laboratory temperature calibration performed just prior to the cruise indicated that the primary PRT was within 0.0005°C of the bath standard. No adjustment was made for a temperature offset.

Pressure

The pressure sensor read high by 4.7db at the surface, and this amount was subtracted from all pressures throughout the cruise.

Salinity

Salinity samples taken on each cast showed the salinity reading from the system to be low by 0.028-0.029psu during the first few stations. The constants in the acquisition system had already been set to compensate for a raw salinity that was low by 0.018psu. Thus, another 0.011psu were added to the salinity calculated using these constants.

Note: the cruise report goes on to say that the CTD was re-calibrated after station 53. Archived data for stations 1-53 were re-calculated using the new calibration.

BODC Data Processing

No further calibrations were applied to the data received by BODC. BODC were mainly concerned with the screening and banking of the data. BODC have not received the CTD data from casts 218 and 241.

The CTD data were received as 1db averaged pressure sorted down cast data. Parameters were pressure (dbar), temperature (its-90) and salinity (pss-78).

The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the graphics editor. Spikes in the data were manually flagged 'suspect' by modification of the associated quality control flag. In this way none of the original data values were edited or deleted during quality control.

Some files had bad final few cycles where pressure was over ~500db and these cycles were deleted. Also, had to edit out from 10-70db for cast 6 because T+S were corrupt.

Very little flagging was required for these data.

Once screened, the CTD data were loaded into a database under the Oracle relational database management system. The start time stored in the database is the CTD deployment time, and the end time is the start time + 60 minutes. 1 day was subtracted from all these times after comparison with the cruise report.

World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

WOCE had two major goals:

Goal 1. To develop models to predict climate and to collect the data necessary to test them.

Goal 2. To determine the representativeness of the Goal 1 observations and to deduce cost effective means of determining long-term changes in ocean circulation.

UK WOCE

The UK made a substantial contribution to the international World Ocean Circulation Experiment (WOCE) project by focusing on two important regions:

VIVALDI, a seven year programme of seasonally repeated surveys to study the upper ocean.

Long-term observations of ocean climate in the North West Approaches.

Satellite ocean surface topography, temperature and wind data were merged with in situ observations and models to create a complete description of ocean circulation, eddy motion and the way the ocean is driven by the atmosphere.

The surveys were forerunners to the international Global Ocean Observing System (GOOS). GOOS was later established to monitor annual to decadal changes in ocean circulation and heat storage which are vital in the prediction of climate change.

Fixed Station Information

Station Name

WOCE Atlantic Area 10 (AR10)

Category

Offshore area

Latitude

27° 0.00' N

Longitude

32° 30.00' W

Water depth below MSL

World Ocean Circulation Experiment (WOCE) Atlantic Area 10 (AR10)

WOCE was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate. WOCE established numerous areas and repeat sections in the Atlantic Ocean as illustrated in the map below.

The AR10 'Beta-triangle' experiments where centred at 27.0°N, 32.5°W in the southwestern end of the North Atlantic subtropical gyre, with the area occupied between May 1992 to May 1993. A table of all AR10 cruises is presented below: